This invention relates to acoustic transducers and more particularly to fiber optic acoustic transducers.
There are many requirements for sensing and measuring acoustic waves, including hydrophones which are employed to sense the noise generated by ships and submarines in the ocean. In order to cover large areas of the ocean huge quantities of hydrophones must be employed. It is thus important that the cost of the hydrophones be kept to a minimum and that the sensitivity thereof be maximized.
In order to meet these requirements, extensive investigation has been undertaken in looking at new technology which may be applicable, including fiber optics. One proposed fiber optic transducer operates on the principle of utilizing change in fiber density or length to produce optical signal phase shifts. In this transducer the fiber undergoes a change in density due to incident acoustic waves which results in a change in refractive index such that any input signal applied thereto will be shifted in phase. Measurement of the acoustic waves is thus accomplished by comparing the phase shifted signal with a reference. This type of transducer, however, has many drawbacks including the requirement that the input signal thereto be coherent and, of course, coherent sources are both expensive and complex. Detection of the acoustic waves in this manner is also costly and complex in that relatively complex phase shift measurements must be made.
Accordingly, it is an object of this invention to provide an acoustic signal transducer which is relatively simple in construction and requires minimum processing of its output signals.